DE69121134T2 - Supported catalyst for the gas phase polymerization of ethylene - Google Patents

Abstract

The present invention relates to a catalyst and a process for preparing a catalyst suitable for polymerization of olefins. The process is carried out in a hydrocarbon liquid medium and comprises successively contacting a refractory oxide support with (a) a dialkylmagnesium optionally with a trialkylaluminium, (b) a particular monochloro organic compound, (c) a titanium and/or vanadium compound(s), and then (d) with ethylene optionally mixed with a C3-C8 alpha-olefin in the presence of an organo-aluminium or organozinc compound to form a prepolymerised catalyst. The catalyst has a high activity, particularly in a gas phase polymerization of ethylene, and has a great ability of copolymerizing alpha-olefins with ethylene.

Description

The present invention relates to a solid catalyst of the Ziegler-Natta type suitable for the polymerization or copolymerization of olefins and relates to a process for the preparation of the catalyst.

It is known that catalyst systems of the Ziegler-Natta type for the polymerization of olefins consist of a solid catalyst comprising at least one compound of a transition metal belonging to group IV, V or VI of the Periodic Table of the Elements and a cocatalyst comprising at least one organometallic compound of a metal belonging to group II or III of the Periodic Table of the Elements. A highly active solid catalyst comprising at least one compound of a transition metal such as titanium and a magnesium compound such as magnesium chloride is preferably used. The cocatalyst is usually selected from organoaluminum or organozinc compounds.

EP-A-0 133 383 discloses a polyolefin supported catalyst for the polymerization of ethylene at temperatures greater than 150°C, for example in a solution process or a high pressure process. The catalyst is obtained by treating a dehydrated particulate support material with (a) a dihydrocarbyl magnesium, (b) a transition metal compound and (c) ethylaluminum dichloride. The catalyst thus obtained can be prepolymerized with at least one α-olefin having 4 to 18 carbon atoms.

Furthermore, a process for preparing a solid catalyst is known from EP-A-0 014 523, which consists in reacting an organomagnesium compound in a liquid hydrocarbon medium with a support based on an inorganic oxide, a "halogenating agent" and a compound of a transition metal, in the presence of a Lewis base. The "halogenating agent" is selected from a variety of products, including hydrogen halides, Silicon halides, carboxylic acid halides, phosphoric acid pentachloride, thionyl chloride, sulphuryl chloride, phosgene, nitrosyl chloride, halides of mineral acids, chlorine, bromine, chlorinated polysiloxanes, hydrocarbon aluminium halides, aluminium chloride, ammonium hexafluorosilicate and hydrocarbon halides such as carbon tetrachloride, chloroform, ethylene chloride, ethylene dichloride or 1,1,1-trichloroethane. However, it has been found that when such halogenating agents are used, the solid catalysts generally have moderate activity in olefin polymerisation. It has also been observed that certain halogenating agents, such as hydrogen halides, are extremely corrosive to metals and require the use of special and expensive equipment. Furthermore, it has been found that during the catalyst preparation, the liquid hydrocarbon medium can be contaminated by the halogenating agent used, either because the latter has not been completely consumed during the reaction or because it leads to the formation of new chlorine-containing compounds which are soluble in this medium and which are difficult to separate from the latter. It then becomes necessary to apply a special treatment for purifying the liquid hydrocarbon medium in each catalyst preparation.

The catalysts of EP-A-0 014 523 are described for use in a process for the polymerisation of α-olefin in the gas phase, for example by means of a fluidised bed reactor, in which the polymer particles formed are maintained in the fluidised state by means of a reaction gas mixture containing the olefin or olefins to be polymerised and are transported as an upward flow at a speed sufficiently high to effectively remove the heat of polymerisation and to maintain the bed in the fluidised state. However, it has been observed that in the polymerisation of olefins these catalysts produce polymer particles which, above a certain size or above a certain degree of polymerisation progress, tend to break off and form particles of undesirable shape and size and relatively low bulk density. It has also been found that this phenomenon is even more pronounced when ethylene is to be polymerized in the gas phase with an α-olefin containing, for example, 3 to 8 carbon atoms.

Another major disadvantage of the process of EP-A-0 014 523 stems from the fact that under conditions for gas phase copolymerization of ethylene with an α-olefin containing 3 to 8 carbon atoms, these catalysts require a relatively high partial pressure of the α-olefin in the reaction gas mixture for a given amount of α-olefin to be fixed in the copolymer. A high pressure of this α-olefin in the reaction gas mixture increases the losses, especially of these expensive starting materials, when the copolymer powder is recovered and degassed outside the polymerization reactor.

A process has now been found for preparing a solid catalyst of the Ziegler-Natta type supported on a refractory oxide which shows a very high activity in olefin polymerization. In addition, this catalyst is prepared under conditions such that the above-mentioned disadvantages in catalyst preparation can be reduced. In particular, the catalyst can be prepared using a conventional plant and in the presence of a liquid hydrocarbon medium which does not require purification treatment after each catalyst preparation. The catalyst also has a structure designed such that the gas phase polymerization of ethylene can be carried out to a high degree of conversion with a reduced risk of bursting of the polymer particles and lowering of the bulk density of the polymer powder. In the conditions of a gas phase copolymerization of ethylene with at least one α-olefin containing 3 to 8 carbon atoms to produce an ethylene copolymer of a given α-olefin(s) content, the use of this solid catalyst also makes it possible to significantly reduce the partial pressure of the α-olefin(s) in the reaction mixture compared to previously known catalysts. This advantage not only enables the improvement of industrial operating conditions of the gas phase copolymerization process, but also the production of ethylene copolymers which, with respect to a given proportion of α-olefin(s) to ethylene in the reaction gas mixture, have a density which is significantly reduced compared to that for already known catalysts.

The present invention relates to a process for preparing a solid catalyst which can be used for the polymerization or copolymerization of olefins, in particular ethylene, the catalyst comprising atoms of magnesium, chlorine, titanium and/or vanadium and a solid support based on a refractory oxide, the process being characterized in that it comprises:

a) in a first step, bringing into contact a solid support of a refractory oxide containing hydroxyl groups with a dialkylmagnesium, optionally mixed or complexed with a trialkylaluminium,

b) in a second stage, bringing the product from the first stage into contact with an organic monochloro compound selected from secondary or tertiary alkyl or cycloalkyl monochlorides containing 3 to 19 carbon atoms and from compounds of the general formula R⁹9 R¹⁰ R¹¹ CCl, where R⁹9 is an aryl radical having 6 to 16 carbon atoms and R¹⁰ and R¹¹ are identical or different radicals selected from hydrogen, alkyl radicals having 1 to 6 carbon atoms and aryl radicals having 6 to 16 carbon atoms, which are identical or different with respect to R⁹9,

(c) in a third stage, bringing the product from the second stage into contact with at least one tetravalent titanium or vanadium compound or one trivalent vanadyl compound and

d) in a fourth step, bringing the product from the third step into contact with ethylene or ethylene mixed with an α-olefin containing 3 to 8 carbon atoms in the presence of at least one activating agent selected from organoaluminium and organozinc compounds, in such amounts that a solid catalyst in the form of a prepolymer containing 1 to 200 g, preferably 10 to 200 g of a (co)polymer of ethylene per milliatom of titanium, or vanadium, or titanium plus vanadium, is obtained, and that the molar ratio of the amount of metal(s) (Al and/or Zn) of the activating agent to the amount of titanium or vanadium or titanium plus vanadium is 0.3 to 10, each of the 4 stages being carried out in a liquid hydrocarbon medium.

The first 3 stages produce a solid intermediate product, particularly catalytically active, comprising in particular a magnesium chloride compound obtained from a specific chlorine source and also at least one compound of titanium or vanadium in its maximum valence of 4 or vanadium in its maximum valence of 5 in the vanadyl group, these elements being fixed on a solid support based on a refractory oxide. However, this solid intermediate product shows disadvantages of catalysts supported on a refractory oxide in that they produce (co)polymers of ethylene of low bulk density in a gas phase polymerization process. The fourth step of the process according to the invention consists in converting the disadvantageous solid intermediate into a special catalyst prepolymerized with ethylene, which has significant improvements in the gas phase (co)polymerization of ethylene, in particular for the easier copolymerization of α-olefins containing 3 to 8 carbon atoms with ethylene.

The refractory oxide-based solid support contains functional hydroxyl groups and may have a specific surface area (BET) of 50 to 1000 m²/g, for example 100 to 600 m²/g and a pore volume of 0.5 to 5 ml/g, for example 1 to 3 ml/g.

The amount of hydroxyl groups in the carrier depends on the carrier used, its specific surface area, the physicochemical treatment and the drying to which it has been previously subjected. A carrier that is ready for use generally contains 0.1 to 5, preferably 0.5 to 3 mmol hydroxyl groups per gram. The support, which may be granulated, is preferably anhydrous at the time of its use in the catalyst preparation. For this purpose, it can preferably be freed of unbound water in a manner known per se, for example by heat treatment in the range from 100°C to 950°C, eg 150°C to 700°C. The support can, for example, be selected in particular from a silica, an alumina, a silica-alumina or a mixture of these oxides and can consist of particles with a mass average diameter in the range from 20 to 250 µm, preferably 30 to 200 µm, in particular 50 to 150 µm. The use of a silica is preferred, particularly one supplied by Crosfield Company (UK) under the trade designation "SD 490" or by WR Grace Company (USA) under the trade designation "SG 332" or a microsphered silica gel supplied by WR Grace Company (USA) under the trade designation "SD 3217".

The first step in the preparation of the solid catalyst consists in bringing the solid support into contact with a dialkylmagnesium of the general formula

Mg R¹ R²

- optionally mixed or complexed with a trialkylaluminium of the general formula

Al R³ R�sup4; R�sup5;

where in the formulas R¹, R², R³, R⁴ and R⁵ are identical or different alkyl radicals having 1 to 12 carbon atoms, preferably having 2 to 8 carbon atoms, where the amount of trialkylaluminum used preferably does not exceed a molar ratio of 1/1, based on the dialkylmagnesium, in particular the molar ratio is 0.01/1 to 1/1, for example 0.1/1 to 0.5/1. Dibutylmagnesium, dihexylmagnesium, butylethylmagnesium, ethylhexylmagnesium or butyloctylmagnesium are preferably used.

When the dialkylmagnesium is used with a trialkylaluminium, an addition compound of the general formula

MgR¹R² x AlR³R&sup4;R&sup5;

are prepared beforehand, in which formula R¹, R², R³, R⁴ and R⁵ are as defined above and x is a number equal to or less than 1, in particular 0.01 to 1, for example 0.01 to 0.5. The addition compound is prepared according to known methods, such as heating a mixture of dialkylmagnesium and trialkylaluminium in solution in a liquid hydrocarbon medium to a temperature preferably in the range of 30 to 100°C. An addition compound of dibutylmagnesium with triethylaluminium or also dihexylmagnesium with triethylaluminium or also butyloctylmagnesium with triethylaluminium is preferably used.

In all cases, dialkylmagnesium and, if present, trialkylaluminium or the addition compound is preferably added in the first stage in the form of a solution in a liquid hydrocarbon, for example alkane or cycloalkane, such as n-hexane or n-heptane.

The first stage, like the other three stages of catalyst preparation, is carried out in a liquid hydrocarbon medium consisting of at least one saturated liquid hydrocarbon, for example an alkane or cycloalkane having 4 to 12 carbon atoms, for example 4 to 8 carbon atoms, such as n-butane, n-pentane, isopentane, n-hexane, n-heptane or cyclohexane, this hydrocarbon being inert to the various compounds involved in the preparation of the solid catalyst. The liquid hydrocarbon medium may be the same or different in each stage of catalyst preparation.

During the first step, dialkyl magnesium and trialkyl aluminum, if applied, are fixed on the solid support. This fixing may occur simultaneously from a reaction between the hydroxyl groups of the solid support and the organometallic compound and from a physicochemical absorption, probably partly due to the organometallic compound being complexed with some oxygen atoms of the refractory oxide. These organometallic compounds may themselves be present on the support in complexed form. fixed, in particular in dimeric or trimeric form. A support can generally be evaluated using its total capacity for fixing a dialkylmagnesium and optionally a trialkylaluminium. Its maximum fixing capacity depends on the nature of the support, on its specific surface, on the physicochemical treatment and on the drying of the support which has been carried out beforehand. The maximum fixing capacity of a support can generally be 1 to 5, preferably 1 to 3 mmoles of dialkylmagnesium, for example dibutylmagnesium or trialkylaluminium per gram of support.

The molar amount of dialkylmagnesium and optionally trialkylaluminium to be used may be less, equal or an excess based on the number of moles of hydroxyl groups present in the support. However, in order to avoid using an excessive amount of dialkylmagnesium and optionally trialkylaluminium, the amount of these compounds will generally be slightly higher than the maximum amount capable of being fixed by the solid support. Thus, in the first step of the process, it is preferred to contact each gram of support with an amount of dialkylmagnesium or dialkylmagnesium plus trialkylaluminium corresponding to 0.1 to 7.5 mmol, preferably 0.5 to 4.5 mmol or more preferably 1 to 3.5 mmol.

The first step can be carried out in various ways. It is possible, for example, to add the dialkylmagnesium and optionally the trialkylaluminium to the solid support, which has preferably been previously suspended in the liquid hydrocarbon medium. This addition can be carried out slowly, for example over a period of 10 to 300, e.g. 30 to 120 minutes, with agitation, e.g. stirring, and at a temperature of 0°C to 80°C, e.g. 10 to 60°C. When a dialkylmagnesium and a trialkylaluminium are used together, their contact with the solid support can be achieved either by gradual addition of the two organometallic compounds in any order or by addition of the mixture or the previously formed Complex of these two organometallic compounds to the liquid hydrocarbon medium containing the solid carrier.

A significant excess of organometallic compound not fixed in the support can be removed by filtration and/or by one or more liquid hydrocarbon washes. However, it has been found that it is possible to use a molar amount of dialkylmagnesium and optionally trialkylaluminium which, according to the maximum fixing capacity of the support, can reach up to 1.5 times the amount of organometallic compounds, without it being absolutely necessary to subsequently remove the excess of organometallic compounds not fixed on the support. Surprisingly, it has been found that under these conditions the possible small excess amount of organometallic compounds not fixed on the support does not interfere in any way with the catalyst preparation and that essentially no fine particles are formed during the subsequent steps.

The second stage of preparing the solid catalyst consists in bringing the solid product resulting from the first stage into contact with an organic monochloro compound. This compound can be a secondary or preferably tertiary alkyl monochloride containing 3 to 19, preferably 3 to 13, carbon atoms and preferably having the general formula

R⁶ R⁶ R⁶ R⁶ CCl

where R6 and R7 are identical or different alkyl radicals having 1 to 6, e.g. 1 to 4, carbon atoms, such as methyl, ethyl or n-propyl, and R8 is a hydrogen atom or preferably an alkyl radical having 1 to 6, e.g. 1 to 4, carbon atoms, identical or different from R6 and R7, such as methyl, ethyl or n-propyl. Secondary propyl chloride, secondary butyl chloride, but especially tert-butyl chloride, are preferred.

The organic monochloro compound can also be a secondary or preferably tertiary cycloalkyl monochloride of the general formula

where R⁸ is a hydrogen atom or preferably an alkyl radical having 1 to 6, e.g. 1 to 4, carbon atoms, such as methyl or ethyl, and n is a number from 4 to 8, e.g. 5 to 8, in particular 5, such as cyclohexyl chloride or 1-methyl-1-chlorocyclohexane.

The organic monochloro compound can also be a compound which contains at least one aryl radical of the general formula: R⁹9 R¹⁰ R¹¹ CCl, where R⁹ is an aryl radical with 6 to 16, e.g. 6 to 10, carbon atoms and R¹ and R¹¹ are identical or different radicals, selected from hydrogen, alkyl radicals with 1 to 6, e.g. 1 to 4 carbon atoms, such as methyl, ethyl or n-propyl, and aryl radicals with 6 to 16, e.g. 6 to 10 carbon atoms, identical or different from R⁹. The aryl radicals for R⁹9, R¹⁰ and/or R¹¹ are usually aromatic hydrocarbon groups, such as phenyl, tolyl or naphthyl. Benzyl chloride and 1-phenyl-1-chloroethane may be preferred.

It has surprisingly been found that the chlorination of the organometallic compounds fixed in the solid support is significantly improved by the use of secondary or tertiary alkyl or cycloalkyl monochlorides or the use of monochloroorgano compounds containing at least one aryl radical, compared with the use of hydrocarbon polychlorides, in particular carbon tetrachloride.

Due to its unexpected behavior, the organic monochloro compound can be used in relatively small amounts during this stage and still allows to form a solid product that is essentially free of basic functional groups capable of subsequently reducing a compound of a transition metal, such as tetravalent titanium, used during the third stage. The proportion of residual, reductive basic functional groups is such that less than 10%, preferably less than 5% of the transition metal of the solid intermediate resulting from the third step is in the reduced state.

The product resulting from the first stage may be brought into contact with the organic monochloro compound in an amount such that the molar ratio of the amount of organic monochloro compound to the amount of magnesium or magnesium plus aluminum contained in the product resulting from the first stage is 1 to 3.5, preferably 1.5 to 3.0.

It has been surprisingly found that when this particular amount of organic monochloro compound is used, the product resulting from the second stage can contain reduced amounts of basic functional groups capable of reducing a compound of a transition metal to its maximum valence, or can contain hardly any, or in particular none, as compared to when the corresponding amounts of hydrocarbon polychlorides are used. The residual amount (if any) of organic monochloro compound at the end of this stage is practically nothing or negligible and usually does not exceed about 1000 parts per million (ppm) by weight in the liquid hydrocarbon medium. It is thus no longer necessary to wash the product resulting from the second stage and to purify the liquid hydrocarbon medium after each catalyst preparation.

The second stage is carried out in the liquid hydrocarbon medium by bringing the organic monochloro compound into contact with the product resulting from the first stage at a temperature in the range of 0°C to 90°C, preferably 20°C to 60°C. The operation can be carried out in various ways, for example by adding the organic monochloro compound to the product resulting from the first stage in suspension in the liquid hydrocarbon medium. This addition is preferably carried out slowly, for example over a period of 10 to 600 minutes, e.g. 20 to 300 minutes, and with agitation, e.g. stirring.

The third stage of the preparation of the solid catalyst consists in bringing the product resulting from the second stage into contact with at least one compound of titanium or vanadium with a maximum valence of 4 or with a vanadyl compound with vanadium with a valence of 5. These titanium or vanadium compounds are preferably soluble in the liquid hydrocarbon medium in which the catalyst is prepared. It is possible in particular to use a tetravalent titanium compound of the general formula

Ti(OR)m X4-m

a tetravalent vanadium compound of the general formula

V (OR)m X4-m

or a vanadyl compound of the general formula

VO (OR)n X3-n

where in the formulas R is an alkyl radical with 1 to 6, e.g. 2 to 6, such as 2 to 4, carbon atoms, e.g. methyl, ethyl, propyl, isopropyl or butyl, X is a chlorine or bromine atom, m is a whole or fractional number equal to or greater than 0 and less than 4, e.g. 0 to 3, and n is a whole or fractional number equal to or greater than 0 and less than 3, e.g. 0 to 2.

The use of titanium tetrachloride is preferred.

The contact is made in the liquid hydrocarbon medium in such a way that a maximum amount of titanium and/or vanadium compounds can be fixed in the support by impregnation, preferably avoiding any reduction of these transition metals, since this generally leads to a reduction in the activity of the catalyst in the ethylene (co)polymerization. For this reason, the product resulting from the second stage is generally free from any basic functional group capable of reducing a titanium and/or vanadium compound. Surprisingly, it has also been found that the product obtained under the particular circumstances of chlorination during the second stage is particularly capable of fixing a large amount of titanium and/or vanadium compounds. This makes it possible to use the product resulting from the second stage into contact with the titanium and/or vanadium compound(s) in an amount substantially less than that used during the impregnation step described in EP-A-0 014 523, in particular in an amount such that the atomic ratio of the amount of titanium or vanadium or titanium plus vanadium contained in the product resulting from the second stage to the amount of magnesium or magnesium plus aluminium is 0.1 to 0.9, preferably 0.2 to 0.7. This fixes most, if not all, of the amount of titanium and/or vanadium compound(s) employed in the carrier, preferably with an unchanged valence state. At the end of this stage, the amount of titanium and/or vanadium compound(s) remaining in the free state in the liquid hydrocarbon medium may be relatively small or negligible. Advantageously, in certain cases it is no longer necessary to wash the solid product resulting from the third stage.

The third stage is generally carried out at a temperature in the range of 0 to 150°C, preferably 20 to 120°C. The operation can be carried out in various practical ways. For example, the titanium and/or vanadium compound(s) can be added to the product resulting from the second stage in suspension in the liquid hydrocarbon medium. This addition is preferably carried out slowly, for example over a period of 10 to 300 minutes, e.g. 20 to 200 minutes, and with agitation, e.g. stirring.

In a preferred embodiment, the third stage can be carried out in a manner which advantageously makes it possible to obtain a solid catalyst with particularly high activity in ethylene polymerization or copolymerization and to provide ethylene (co)polymers with a narrow molecular weight distribution. It essentially consists in bringing the product from the second stage into contact, firstly, with at least one halogen-rich titanium or vanadium compound and then with at least one titanium or vanadium compound containing little or no halogen. preferably at least one alkoxide-rich titanium or vanadium compound. The halogen-rich titanium or vanadium compound is in particular a tetravalent titanium compound of the general formula

Ti(OR)p X4-p

a tetravalent vanadium compound of the general formula

VO (OR)p X4-p

and a vanadyl compound of the general formula

VO (OR)q X3-q

where R and X in the formulas have definitions that are the same as those mentioned above, p is a whole or fractional number equal to or greater than 0 or less than 2, e.g. 0 to 1.5 or 0 to 1, and q is a whole or fractional number equal to or greater than 0 and less than 1.5, e.g. 0 to 1 or to 0.5. The halogen-rich titanium or vanadium compound is preferably titanium tetrachloride, vanadium tetrachloride or vanadyl trichloride. The use of titanium tetrachloride is preferred.

The alkoxide-rich titanium or vanadium compound containing little or no halogen is selected in particular from a tetravalent titanium compound of the general formula

Ti(OR)r X4-r

a tetravalent vanadium compound of the general formula

V (OR)r X4-r

and a vanadyl compound of the general formula

VO (OR)s X3-s

where R and X in the formulas have definitions which are the same as those mentioned above, r is an integer or fractional number equal to or greater than 2 and less than or equal to 4, eg 2.5 to 4 or 3 to 4, and s is an integer or fractional number equal to or greater than 1.5 and less than or equal to 3, eg 2 to 3 or 2.5 to 3. In particular, the alkoxide-rich compound which contains little or no halogen is preferably a titanium tetraalkoxide, a vanadium tetraalkoxide and a vanadyl trialkoxide, in particular titanium or vanadium tetraisopropoxide, titanium or vanadium tetra-n-propoxide, titanium or vanadium tetrabutoxide, titanium or vanadium tetraethoxide, vanadyl tri-n-propoxide, vanadyl tributoxide and vanadyl triethoxide.

The ratio of alkoxide-rich titanium or vanadium compounds containing little or no halogen relative to the halogen-rich ones used in this step can be designed such that the molar ratio of the former to the latter is 0.1 to 3, preferably 0.2 to 2.

The conditions under which the two successive contacts are carried out correspond to those defined above for the single contact. In particular, the total amount of titanium and/or vanadium compounds is such that the atomic ratio of the total amount of titanium or vanadium or titanium plus vanadium to the amount of magnesium or magnesium plus aluminum contained in the product resulting from the second stage is 0.1 to 0.9, preferably 0.2 to 0.7.

The solid product resulting from the third stage comprises a support based on a refractory oxide containing halogenated compounds of magnesium, tetravalent titanium and/or vanadium and/or trivalent vanadyl. The atomic ratio between the amount of magnesium and the amount of titanium and/or vanadium in the solid product can generally be 2 to 8, preferably 2.5 to 5.

The fourth stage of the preparation of the solid support consists in bringing the solid product resulting from the third stage, also called solid intermediate, into contact with ethylene or ethylene mixed with an α-olefin containing from 3 to 8 carbon atoms, in the presence of at least one organoaluminium or organozinc compound. The contact can be carried out batchwise or continuously and is preferably carried out by adding the solid product resulting from the third stage, in suspension in the liquid hydrocarbon medium, ethylene and optionally an α-olefin containing from 3 to 8 carbon atoms, for example propylene, butene-1, hexene-1, methyl-4-pentene-1 or octene-1. preferably at a constant, slow flow rate and for a period of time such that the solid catalyst is in the form of a prepolymer containing 1 to 200 g, preferably 10 to 200 g, eg 20 to 100 g of polymer per milliatom of titanium or vanadium or titanium plus vanadium. The α-olefin optionally used mixed with the ethylene is used in a smaller amount compared to ethylene, preferably such that the proportion of copolymerized α-olefin in the prepolymer is not higher than 10 wt.% and preferably 0.1 to 7 wt.%, based on ethylene. The ethylene prepolymerized catalyst thus obtained at the end of the fourth stage comprises a (co)polymer of ethylene with relatively high crystallinity and low solubility in liquid hydrocarbon and provides a particularly high capacity for the incorporation of C3 to C8 α-olefins into an ethylene copolymer during copolymerization. The contact in the fourth stage can generally be made by agitation, e.g. stirring, at a temperature generally between 10 and 100°C, preferably between 40°C and 90°C and at a pressure generally higher than atmospheric pressure and lower than 2 MPa, e.g. 0.2 to 1 MPa. The duration of this contact can be 10 to 900 minutes, e.g. 30 to 600 minutes.

This contact can advantageously be made in the presence of hydrogen, which is added to the reaction mixture once at the start of the contact or at other times or even slowly at a constant flow rate while the contact is being made. The amount of hydrogen used during this stage is such that the partial pressure of hydrogen can be 0.01 to 1 MPa, for example 0.05 to 0.5 MPa. The presence of hydrogen during this stage, even in a very small amount, makes it possible to subsequently produce ethylene polymers or copolymers with a perfectly homogeneous composition, in particular free of gels.

The contact in the fourth stage is made in the presence of an activating agent selected from organoaluminium compounds, such as trialkylaluminium or alkylaluminium hydrides, chlorides and alcoholates or organozinc compounds such as diethylzinc. The activating agent may be added to the liquid hydrocarbon medium either all at once at the beginning of the contact or at various times distributed between the beginning and the end as the contact is established. The amount of activating agent employed during this step is such that the atomic ratio between the amount of metal(s) (Al and/or Zn) of the activating agent and the amount of titanium or vanadium or titanium plus vanadium is 0.3 to 10, preferably 0.7 to 5, for example 0.8 to 3.

An electron donor compound, such as a Lewis base, may be used during any of the four steps, but is not essential. On the other hand, it is better not to use a compound of this type, since its presence lowers the activity of the solid catalyst in the ethylene (co)polymerization. Preferably, the electron donor compound is substantially absent. The amount of electron donor compound, if used in the preparation of the solid catalyst, may be limited to very small proportions, in particular such that the molar ratio of the amount of electron donor compound to the amount of titanium or vanadium or magnesium plus vanadium is less than 1/5, for example 0 to 0.2, preferably 1/10, for example 0 to 0.1, and that the molar ratio of the amount of electron donor compound to the amount of magnesium or magnesium plus aluminium is less than 1/10, for example 0 to 0.1, preferably less than 1/20, for example 0 to 0.05. The electron donor compound may be an organic electron donor compound free of labile hydrogen, for example selected from ether, thioether, amine, amide, phosphine, sulphoxide, phosphoramide, silane or ester.

The catalyst obtained after this last step is a solid ethylene prepolymerized catalyst of the Ziegler-Natta type, based on titanium and/or vanadium, which can be used for the polymerization or copolymerization of olefins. It comprises the essential elements, which are already present in the intermediate product obtained at the end of the third stage in similar proportions, in particular a refractory oxide and atoms of chlorine, magnesium, titanium and/or vanadium and additionally comprises an organoaluminium compound and/or an organozinc compound. More specifically, this catalyst comprises per milliatom of titanium or vanadium or titanium plus vanadium 1 to 200 g, preferably 10 to 200 g of polyethylene or a copolymer of ethylene with a minor amount of an α-olefin containing 3 to 8 carbon atoms, 0.2 to 15 g, preferably 0.3 to 10 g, of a refractory oxide, 1 to 10, preferably 1.4 to 5 milliatoms of magnesium, 0.1 to 20, preferably 0.3 to 10 milliatoms of aluminum or zinc or aluminum plus zinc and 0 to a value less than 0.2, preferably 0 to 0.1, e.g. 0.001 to 0.08 mmol of an electron donor compound. This solid catalyst is in the form of non-sticky particles having a mass average diameter of 50 to 500 µm, preferably 80 to 400 µm, for example 100 to 300 µm and a bulk density in the range of 0.25 to 0.60, preferably 0.3 to 0.5, for example 0.4 to 0.5 g/cm³.

The solid catalyst obtained at the end of the fourth stage can advantageously be washed once or several times with a liquid hydrocarbon, for example an alkane such as n-hexane, and can be used as such directly in a gas phase ethylene polymerization or copolymerization, in particular in a fluidized bed reactor. It can, if desired, be isolated from the liquid hydrocarbon medium in which it was prepared or with which it was washed, for example by evaporating the latter, at a temperature ranging up to 100°C, for example 10 to 80°C, and optionally under partial vacuum.

The solid catalyst prepared according to the invention is particularly suitable for the gas phase polymerization of ethylene and in particular for the gas phase copolymerization of ethylene with at least one α-olefin containing 3 to 8 carbon atoms, for example propylene, butene-1, hexene-1, methyl-4-pentene-1 or octene-1, in particular for high-density Polyethylene (density: 0.94 to 0.97 g/cm³) and linear low density polyethylene or very low density polyethylene (density: 0.88 to 0.94 g/cm³) with 3 to 30%, for example 5 to 25% by weight of C₃ to C₈ α-olefins, for example by means of a fluidized bed reactor at a temperature of 20°C to 110°C, preferably 40 and 100°C and under a total pressure which may vary from 0.5 to 5 mPa, the ratio of the partial pressure of the α-olefin(s) to that of ethylene being 0.01 to 0.5, preferably 0.02 to 0.45, for example 0.03 to 0.43. The solid catalyst is preferably used simultaneously with a cocatalyst. The latter can be selected from organoaluminium and organozinc compounds, which are the same or different from the activating agent used during the fourth stage of the preparation of the catalyst. It is used in the polymerization medium simultaneously with or separately from the solid catalyst in an amount such that the atomic ratio of the metal(s) (Al or Zn) of the cocatalyst to titanium or vanadium or titanium plus vanadium is 0.1 to 10, preferably 0.2 to 5. The gas phase ethylene polymerization or copolymerization carried out in the presence of the solid catalyst prepared according to the invention has the advantage of leading to a high conversion without a significant drop in the bulk density of the polymer or copolymer powder produced (0.32 to 0.45 g/cm3), which may have a Ti and/or V content of 1 to 15 ppm, preferably 2 to 10 ppm.

In order to produce ethylene copolymer with a given α-olefin content, the solid catalyst prepared according to the invention also requires a relatively low proportion of α-olefin with respect to ethylene in the reaction gas mixture used in the gas phase copolymerization. The solid catalyst of the present invention allows the special feature of incorporating a relatively high proportion of C₃-C₈ α-olefin, for example butene-1 or methyl-4-pentene-1, into an ethylene copolymer during a gas phase copolymerization under a total pressure of 1.5 MPa, whereby this characteristic can be expressed by at least one of the following equations:

(1) A = a x (pC4/pC2),

where A is the weight-based butene-1 content of an ethylene/butene-1 copolymer produced at 95°C in a gas phase copolymerization carried out with the catalyst according to the invention in the presence of a reaction gas mixture containing ethylene and butene-1, where (pC4/pC2) is the ratio of the partial pressures of butene-1 to that of ethylene in the reaction gas mixture in the range from to 0.43, preferably 0.01 to 0.36, for example 0.01 to 0.1, and a is a number from 50 to 70, preferably 60 to 70;

(2) B = b x (pC6/pC2),

wherein B is the methyl-4-pentene-1 content by weight of an ethylene/methyl-4-pentene-1 copolymer prepared at 70°C in a gas phase copolymerization carried out with the catalyst of the present invention in the presence of a reaction gas mixture containing ethylene and methyl-4-pentene-1, wherein (pC6/pC2) is the ratio of the partial pressures of methyl-4-pentene-1 to that of ethylene in the reaction gas mixture in the range of 0 to 0.3, preferably 0.01 to 0.25, e.g. 0.01 to 0.1, and b is a number from 80 to 100, preferably 90 to 100.

The following non-limiting examples illustrate the present invention. In Tables 1, 2 and 3 productivity is expressed in grams of (co)polymer per milliatom of Ti or V; MI2,16 is the melt index of the (co)polymer measured according to standard method ASTM-D-1238, condition E, BD is the bulk density of the (co)polymer powder at rest; pC4/pC2 is the ratio of the partial pressure of butene-1 to that of ethylene in the reaction gas mixture.

example 1 Production of a catalyst

A support consisting of silica powder, "SD 490", registered trademark, supplied by Crosfield Company (UK) having a specific surface area (BET) of 300 m²/g and a pore volume of 1.7 ml/g was used. It consists of particles with a mass average diameter of 100 µm. It was dried for 5 hours at 500ºC in an air atmosphere to provide an anhydrous silica powder and containing 1 mmol of hydroxyl group per gram. All subsequent operations were carried out under an inert nitrogen atmosphere.

600 ml of n-hexane and 60 g of the dried silica were introduced into a 1-liter stainless steel reactor equipped with a stirrer rotating at 250 rpm, followed by slow addition of 190 mmol of dibutylmagnesium over 1 hour at a temperature of 20°C. The mixture thus obtained was stirred at 20°C for 1 hour. The solid product (A) thus obtained was washed three times with 600 ml of n-hexane each time at 20°C and after these washings it contained 1.7 milliatoms of magnesium per gram of silica.

The reactor containing the solid product (A) in suspension in 600 ml of n-hexane was then heated to 50°C. 204 mmol of tert-butyl chloride were added to the reactor slowly over 1 hour with stirring. At the end of this time, the mixture was stirred at 50°C for 1 hour and then cooled to room temperature (20°C). The resulting solid product (B) was washed three times with 600 ml of n-hexane each time at 20°C. After these washes, it contained 1.7 milliatoms of magnesium and 2.7 milliatoms of chlorine per gram of silica and essentially no basic functional groups reductive to titanium tetrachloride.

The reactor containing a quantity of solid product (B) containing 30 g of silica suspended in 600 ml of n-hexane was then heated to 25°C. 15.3 mmol of titanium tetrachloride was slowly added to the reactor over 1 hour with stirring. The resulting mixture was stirred at 25°C for 1 hour. 15.3 mmol of titanium tetraisopropoxide was then slowly added over 1 hour with stirring to the reactor which was kept at 25°C. The resulting mixture was then stirred at 25°C for 1 hour and then cooled to room temperature (20°C). The resulting solid product (C) was washed three times with 600 ml of n-hexane each time at 20ºC. After these washes it contained 1.7 milliatoms of magnesium, 3.9 milliatoms of chlorine and 0.45 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 L of n-hexane, 10.8 mmol of tri-n-octylaluminum and a quantity of solid product (C) containing 6 milliatoms of titanium were introduced into a 5 L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70°C. A volume of 280 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, with a continuous flow of 160 g/h for 3 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator, removing n-hexane at 60°C under partial vacuum. The ready-to-use solid catalyst (D) was thus obtained in the form of a prepolymer powder consisting of particles with a mass-average diameter of 250 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 2 Production of a catalyst

The procedure was carried out exactly as in Example 1 to produce solid products (A) and (B).

Then, 600 ml of n-hexane and a quantity of the solid product (B) containing 30 g of silica were introduced into a 1-liter stainless steel reactor equipped with a stirring system rotating at 250 rpm and heated to 50°C, followed by 25.5 mmol of titanium tetrachloride over 1 hour. The resulting mixture was then stirred at 50°C for 1 h and then cooled to room temperature (20°C). The resulting solid product (E) was washed three times with 600 ml of n-hexane each at 20°C. After these washings, it contained 1.7 milliatoms of magnesium, 4.8 milliatoms of chlorine and 0.54 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 l n-hexane, 18 mmol tri-n-octylaluminium and a quantity of solid product (E) containing 6 milliatoms of titanium, were introduced into a 5 l stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70ºC. A volume of 400 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, at a constant flow of 100 g/h for 3 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator where n-hexane was evaporated at 60ºC under partial vacuum. The ready-to-use solid catalyst (F) was thus obtained in the form of a prepolymer powder consisting of particles with a mass average diameter of 220 µm and containing 50 g of polyethylene per milliatom of titanium.

Example 3 Production of a catalyst

The procedure was carried out exactly as in Example 2 to prepare the solid products (A), (B) and (E).

Subsequently, 2 L of n-hexane, 10.8 mmol of tri-n-octylaluminum and a quantity of solid product (E) containing 6 milliatoms of titanium were introduced into a 5 L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70°C. A volume of 400 ml of hydrogen, measured under normal conditions, was then introduced, followed by ethylene, under a constant flow of 160 g/h for 3 hours. At the end of this period, 7.2 mmol of tri-n-octylaluminum was added to the mixture and the reactor was then degassed and its contents transferred to a rotary evaporator where n-hexane was evaporated at 60°C under partial vacuum. The ready-to-use solid catalyst (G) was thus obtained in the form of a powder consisting of particles with a mass-average diameter of 260 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 4 Production of a catalyst

The procedure for preparing the solid product (A) was carried out exactly as in Example 1.

Then, 600 ml of n-hexane and a quantity of the solid product (A) containing 60 g of silica were introduced into a 1-liter stainless steel reactor equipped with a stirrer operating at 250 rpm and heated to 50°C, followed by slow addition of 306 mmol of tert-butyl chloride over 1 hour. At the end of this period, the mixture was stirred at 50°C for 1 hour and then cooled to room temperature (20°C). The obtained solid product (H) was washed three times with 600 ml of n-hexane each time at 20°C. After these washes, it contained 1.6 milliatoms of magnesium and 3.2 milliatoms of chlorine per gram of silica and essentially no functional group reductive to titanium tetrachloride.

The reactor containing a quantity of 30 g of solid product (H) containing silica in suspension in 600 ml of n-hexane was then heated to 50°C. 24 mmol of titanium tetrachloride was slowly added to the reactor over 1 hour with stirring. At the end of this period, the mixture was stirred at 50°C for 1 hour and then cooled to room temperature (20°C). The resulting solid product (1) was washed three times with 600 ml of n-hexane each time at 20°C. After these washings, it contained 1.6 milliatoms of magnesium, 4.25 milliatoms of chlorine and 0.49 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 l of n-hexane, 9.6 mmol of tri-n-octylaluminium and a quantity of the solid product (I) containing 6 milliatoms of titanium were introduced into a 5 l stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70ºC. A volume of 400 ml of hydrogen, measured under normal conditions, was then introduced therein, followed by ethylene, at a constant flow of 160 g/h for 3 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator, evaporating n-hexane at 60ºC under partial vacuum. The ready-to-use solid catalyst (J) was obtained in the form of a prepolymer powder consisting of particles with a mass average diameter of 250 µm and with 80 g polyethylene per milliatom of titanium.

Example 5

600 ml of n-hexane and 60 g of dry silica, identical to that used in Example 1, were introduced into a 1-liter stainless steel reactor equipped with a stirrer rotating at 250 rpm, followed by slow addition of 80 mmol of dibutylmagnesium and 40 mmol of triethylaluminium over 1 hour at a temperature of 20°C. At the end of this period, the mixture was stirred at 20°C for 1 hour. The solid product thus obtained (K) was washed three times each with 600 ml of n-hexane at 20°C and contained 1.1 milliatoms of magnesium and 0.68 milliatoms of aluminum per gram of silica.

The reactor containing the solid product (K) in suspension in 600 ml of n-hexane was then heated to 50°C. 254 mmol of tert-butyl chloride was added to the reactor slowly over 1 hour with stirring. At the end of this period, the mixture was stirred at 50°C for 1 hour and then cooled to room temperature (20°C). The resulting solid product (L) was washed three times with 600 ml of n-hexane each time at 20°C and contained 1.1 milliatoms of magnesium, 0.4 milliatoms of aluminum and 2 milliatoms of chlorine per gram of silica and essentially no basic functional group reductive to titanium tetrachloride.

The reactor containing a quantity of solid product (L) containing 30 g of silica in suspension in 600 ml of n-hexane was then heated to 50°C. 30 mmol of titanium tetrachloride was slowly added to the reactor over 1 hour with stirring. At the end of this period, the mixture was stirred at 50°C for 1 hour and was cooled to room temperature (20°C). The resulting solid product (M) was washed three times with 600 ml of n-hexane each at 20°C and contained 1.1 milliatoms of magnesium, 0.4 milliatoms of aluminum, 3.1 milliatoms of chlorine and 0.4 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 1 n-hexane, 10.8 mmol of tri-n-octylaluminum and a quantity of solid product (M) containing 6 milliatoms of titanium were introduced into a 5-L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70ºC. A volume of 400 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, at a constant flow of 160 g/h for 3 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator where n-hexane was evaporated at 60ºC under partial vacuum. The ready-to-use solid catalyst (N) was thus obtained in the form of a prepolymer powder consisting of particles with a mass-average diameter of 250 µm and containing 80 g of polyethylene per nilliatom of titanium.

Example 6 Manufacturing a catalyst

A support was used consisting of a silica powder, "SG 332", registered trademark, sold by W.R. Grace Company (United States of America) with a specific surface area (BET) of 300 m²/g and a pore volume of 1.7 ml/g. It consisted of particles with a mass average diameter of 80 µm. It was dried for 8 hours at 200ºC under air atmosphere and a silica powder freed from unbound water and containing about 2 mmol of hydroxyl groups per gram was obtained. All subsequent operations were carried out under an inert nitrogen atmosphere.

600 ml of n-hexane and 60 g of the dried silica were introduced into a 1-L stainless steel reactor, equipped with a stirrer rotating at 250 rpm, followed by slow addition of 60 mmol of dibutylmagnesium over 1 hour at a temperature of 20 °C.

The reactor was then heated to 50ºC and 120 mmol of tert-butyl chloride was slowly added over 1 hour with stirring. While the temperature was still maintained at 50ºC, 30 mmol of titanium tetrachloride was introduced. At the end of this introduction, the reactor was heated to 80ºC. and kept at this temperature for 2 hours with stirring. At the end of this period, the reactor was cooled and the solid (O) was obtained containing 0.5 milliatoms of titanium per gram of silica suspended in hexane, with less than 100 ppm (parts per million by weight) of titanium.

2 1 n-hexane, 7.2 mmol of tri-n-octylaluminum and a quantity of solid product (O) containing 6 milliatoms of titanium were introduced to a 5-L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70ºC. A volume of 280 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, at a constant flow of 60 g/h for 4 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator, removing n-hexane at 60ºC under partial vacuum. The ready-to-use solid catalyst (P) was thus obtained in the form of a powder consisting of particles with a mass-average diameter of 250 µm and containing 40 g of polyethylene per milliatom of titanium.

Example 7 Manufacturing a catalyst

A support consisting of a silica powder, "5G 332" registered trademark, sold by W.R. Grace Company (United States of America) with a specific surface area (BET) of 300 m²/g and a pore volume of 1.7 ml/g was used. It consisted of particles with a mass average diameter of 80 µm. It was dried for 8 hours at 200°C and a silica powder, freed of unbound water and containing about 2 mmol of hydroxyl groups per gram, was obtained. All subsequent operations were carried out under an inert nitrogen atmosphere.

600 ml of n-hexane and 60 g of the dried silica were placed in a 1-L stainless steel reactor equipped with a stirrer rotating at 250 rpm, followed by slow addition of 138.6 mmol of dibutylmagnesium within 1 hour at a temperature of 20ºC. The resulting mixture was stirred for 1 hour at 20ºC and a solid product (Q) was obtained.

The reactor was then heated to 50ºC and 277.2 mmol of tert-butyl chloride were slowly introduced over 1 hour with stirring. At the end of this period, the mixture was continued to be stirred for 1 hour at 50ºC and then cooled to room temperature (20ºC). A solid product (R) was obtained in suspension in n-hexane, containing chlorine and magnesium in a Cl/Mg atomic ratio equal to 1.69 and without functional groups reductive to titanium tetrachloride. The liquid phase of this suspension contained 500 ppm of tert-butyl chloride.

The reactor containing the suspension of the solid product (R) in n-hexane was then heated to 50°C. 69.3 mmol of titanium tetrachloride were slowly introduced therein over 2 hours with stirring. The mixture thus obtained was kept stirred at 50°C for 1 hour and then cooled to room temperature. A solid (5) was thus obtained in suspension with n-hexane which, after 3 washes each with 600 ml of n-hexane, contained 2.18 milliatoms of magnesium, 5.7 milliatoms of chlorine and 0.65 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 L of n-hexane, 9.6 mmol of tri-n-octylaluminum and a quantity of solid product (5) containing 6 milliatoms of titanium were introduced into a 5 L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70°C. A volume of 280 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, at a constant flow of 120 g/h for 4 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator where n-hexane was evaporated at 60°C under partial vacuum. The ready-to-use solid catalyst (T) was thus obtained in the form of a prepolymer powder consisting of particles with a mass-average diameter of 250 µm and containing 80 g of polyethylene per nilliatom of titanium.

Example 8 Production of a catalyst

The procedure was carried out exactly as in Example 7 except for the fact that 277.2 mmol of sec-butyl chloride was introduced into the reactor instead of tert-butyl chloride and that the solid products (R1) and (S1) were obtained and used to prepare the solid catalyst (T1) instead of the solid products (R) and (S), respectively.

The solid product (R1) was obtained in suspension in n-hexane and contained chlorine and magnesium in a Cl/Mg atomic ratio equal to 1.57 and contained essentially no functional group reductive to titanium tetrachloride. The liquid phase of this suspension contained 900 ppm of sec-butyl chloride.

The solid product (S1) contained 2.05 milliatoms of magnesium, 5.2 milliatoms of chlorine and 0.58 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

The solid catalysts (T1) were obtained in the form of a prepolymer powder consisting of particles with a mass-average diameter of 250 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 9 Production of a catalyst

The procedure was carried out exactly as in Example 7, except for the fact that 69.3 mmol of vanadyl trichloride were introduced into the reactor instead of titanium tetrachloride. A solid product (S2) was thus obtained in suspension in n-hexane which, after 3 washes, each with 600 ml of n-hexane, contained 2.1 milliatoms of pentavalent vanadium per gram of silica and essentially no tetravalent vanadium.

2 l of n-hexane, 9.6 mmol of tri-n-octylaluminium and a quantity of solid product (S2) containing 6 milliatoms of vanadium were introduced into a 5 l stainless steel reactor equipped with a stirrer rotating at 750 rpm and heated to 70ºC. A volume of 280 ml of hydrogen, measured under normal conditions, were introduced thereto, followed by ethylene, at a constant flow of 120 g/h for 4 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator, where n-hexane was evaporated at 60ºC under partial vacuum. The ready-to-use solid catalysts (T2) were thus obtained in the form of prepolymer powders consisting of particles with a mass average diameter of 250 µm and containing 80 g of polyethylene per milliatom of vanadium.

Example 10 (Comparison) Production of a catalyst

The mixture prepared in Example 7 containing the solid product (Q) was used.

The reactor containing the solid product (Q) was heated to 50°C and 277.2 mmol of n-butyl chloride were slowly added with stirring over 1 hour. At the end of this period, the mixture thus obtained was further stirred at 50°C for 1 hour and then cooled to room temperature. The liquid phase of the suspension thus obtained contained about 50,000 ppm of n-butyl chloride. The solid product (U) contained chlorine and magnesium in a Cl/Mg ratio of about 0.2 as well as some basic functional groups capable of reducing titanium tetrachloride.

The reactor containing the suspension of the solid product (U) in n-hexane was heated to 50°C. 69.3 mmol of titanium tetrachloride was slowly introduced thereto over 2 hours with stirring. The resulting mixture was kept stirred at 50°C for 1 hour and then cooled to room temperature. The solid (V) was obtained as a suspension in hexane and was washed three times with 600 ml of n-hexane each time at 20°C. After these washings, the solid (V) contained 2.0 milliatoms of magnesium, 5.1 milliatoms of chlorine, 0.41 milliatoms of tetravalent titanium and 0.39 milliatoms of trivalent titanium per gram of silica.

2 1 n-hexane, 9.6 mmol of tri-n-octylaluminum and a quantity of solid product (V) containing 6 milliatoms of titanium were added to a 5-l stainless steel reactor equipped with a stirrer rotating at 750 rpm and heated to 70ºC. A volume of 280 ml of hydrogen, measured under normal conditions, was then introduced thereto, followed by ethylene, at a constant flow of 120 g/h for 4 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator, where n-hexane was evaporated at 60ºC under partial vacuum. The ready-to-use solid catalyst (W) was thus obtained in the form of a prepolymer powder consisting of particles with a mass average diameter of 250 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 11 Gas phase polymerization of ethylene in a fluidized bed reactor

800 g of anhydrous and deaerated polyethylene powder were introduced as powder feed into a 20 cm diameter fluidized bed reactor. This powder was fluidized by means of a gas stream consisting of a mixture of ethylene and hydrogen, driven up at a speed of 15 cm/s, at a total pressure of 1.5 MPa. 8 mmol of tri-n-octylaluminum were fed to the reactor, followed by an amount of solid catalyst prepared according to the present invention, equivalent to 0.8 milliatom of titanium. For the solid catalyst (P) only, 8 mmol of triethylaluminum was used instead of tri-n-octylaluminum. The total pressure in the reactor was kept constant and equal to 1.5 MPa by adding ethylene and the polymerization reaction was carried out for 3 to 5 hours.

Table 1 shows, according to the catalysts used, the operating conditions of the ethylene polymerization and the properties of the polyethylene powders obtained. For comparison, instead of introducing catalyst (F) prepared according to the present invention, the solid intermediate (E) was introduced in an amount equivalent in milliatoms to titanium and it was particularly noted that the polyethylene powder obtained with the solid catalyst (F) showed a bulk density significantly higher than that of the Polyethylene obtained with the solid intermediate (E).

Example 12 Gas phase copolymerization of ethylene with 1-butene in a fluidized bed reactor

800 g of anhydrous and deaerated powder of a copolymer of ethylene and 1-butene was introduced as powder feed into a 20 cm diameter fluidized bed reactor. This powder was fluidized by means of an upward gas flow driven at a velocity of 15 cm/s and consisting of a mixture of ethylene, 1-butene and hydrogen at a total pressure of 1.5 MPa. 8 mmoles of tri-n-octylaluminum were fed to the reactor, followed by an amount of solid catalyst prepared according to the present invention equivalent to 0.8 milliatoms of titanium. For the solid catalysts (T), (T1), (T2) and (W), 8 mmoles of triethylaluminum were used instead of tri-n-octylaluminum.

For comparison, instead of introducing the solid catalyst (G) prepared according to the present invention, the solid intermediate (E) was introduced in an amount equivalent in milliatoms to titanium. Also for comparison, instead of introducing the solid catalyst (T) prepared according to the present invention, the solid catalyst (W) of Comparative Example 10 prepared using primary alkyl monochloride was introduced.

Table 2 shows the operating conditions of the copolymerization of ethylene with 1-butene and the properties of the copolymer powders obtained. It was particularly noted that the copolymer powder obtained with the solid catalyst (G) had a bulk density significantly higher than that of the copolymer obtained with the solid intermediate (E). It was also noted that, in order to obtain a copolymer of a certain density, the ratio of partial pressure of 1-butene to that of ethylene was significantly lower in the case of the solid catalyst prepared according to the present invention than in the case of the solid intermediate, prepared according to a process not comprising the fourth step. It was also noted that the productivity of copolymer with the catalyst (T) of the invention was significantly higher than with catalyst (W).

Example 13 Production of a catalyst

The silica powder, "SG 332", registered trademark, sold by W.R. Grace Company (United States of America) was dried for 8 hours at 200°C in an air atmosphere to provide a silica freed from unbound water and containing about 2 mmol of hydroxyl groups per gram. All subsequent operations were carried out under an inert nitrogen atmosphere.

600 ml of n-hexane and 60 g of the dried silica were introduced into a 1-liter stainless steel reactor equipped with a stirrer rotating at 250 rpm, followed by slow addition of 190 mmol of dibutylmagnesium over 1 hour at a temperature of 20°C. The resulting mixture was stirred for 1 hour at 20°C and a solid product containing 1.55 milliatoms of magnesium per gram of silica was obtained. The reactor was then heated to 50°C and 186 mmol of tert-butyl chloride was slowly introduced over 1 hour with stirring. At the end of this period, the mixture was continued to be stirred at 50°C for 1 hour and then cooled to room temperature (20°C). A solid product (X) was obtained in suspension in n-hexane, containing chlorine and magnesium in a Cl/Mg atomic ratio equal to 1.6, and essentially without functional groups reductive to titanium tetrachloride. A liquid phase of this suspension contained 600 ppm tert-butyl chloride.

The reactor containing the suspension of the solid product (X) in n-hexane was then heated to 50°C. 48 mmol of titanium tetrachloride were slowly introduced therein over 2 hours with stirring. The resulting mixture was kept stirred at 50°C for 1 hour and then cooled to room temperature. cooled. A solid product (Y) was thus obtained in suspension in n-hexane which, after three washings each with 600 ml of n-hexane, contained 1.63 milliatoms of magnesium, 5 milliatoms of chlorine and 0.53 milliatoms of tetravalent titanium per gram of silica and essentially no trivalent titanium.

2 L of n-hexane, 9.6 mmol of tri-n-octylaluminum and a quantity of solid product (Y) containing 6 milliatoms of titanium were introduced into a 5 L stainless steel reactor equipped with a stirrer stirring at 750 rpm and heated to 70°C. A volume of 280 ml of hydrogen, measured under normal conditions, was introduced thereto, followed by ethylene, with a continuous flow of 120 g/h for 4 hours. At the end of this period, the reactor was degassed and its contents transferred to a rotary evaporator where n-hexane was evaporated at 60°C under partial vacuum. The ready-to-use solid catalyst (Z) was thus obtained in the form of a prepolymer powder consisting of particles with a mass-average diameter of 250 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 14 (Comparison) Production of a catalyst

The procedure was carried out exactly as in Example 13, except that 186 mmol of carbon tetrachloride was introduced into the reactor instead of tert-butyl chloride and that the solid products (X1) and (Y1) were obtained and used to prepare a solid catalyst (Z1) instead of the solid products (X) and (Y).

The solid product (X1) was obtained in suspension in n-hexane and contained chlorine and magnesium in a Cl/Mg atomic ratio equal to 0.97 and functional groups that act reductively towards titanium tetrachloride. The liquid phase of this suspension contained a quantity of chlorine-containing organic compounds.

The solid product (Y1) contained 1.72 milliatoms of magnesium, 3.4 milliatoms of chlorine, 0.45 milliatoms of tetravalent titanium and 0.1 milliatoms of trivalent titanium per gram of silicon dioxide.

The solid catalyst (Z1) was obtained in the form of a prepolymer powder consisting of particles having a mass average diameter of 250 µm and containing 80 g of polyethylene per milliatom of titanium.

Example 15 Gas phase polymerization of ethylene in a fluidized bed reactor

The procedure was carried out exactly as in Example 12 except for using the solid catalyst (Z). For comparison, instead of using the solid catalyst (Z) prepared according to the invention, the solid catalyst (Z1) was used.

Table 3 shows the operating conditions of the ethylene polymerization and the properties of the obtained polyethylene powders. It was particularly found that the productivity of the solid catalyst (Z1) was noticeably lower than that of the solid catalyst (Z)

Example 16 Gas phase polymerization of ethylene with butene-1 in a fluidized bed reactor

The procedure was carried out exactly as in Example 12, except for the use of the solid catalyst (P) in an amount equivalent to 0.8 milliatom of titanium, using 8 mmol of tri-n-octylaluminum at a temperature of 95°C with a mixture of ethylene, butene-1 and hydrogen containing 10% (by volume) of hydrogen, the ratio (pC₄/pC₂) of the partial pressure of butene-1 to that of ethylene being 0.03.

Under these conditions, a copolymer of ethylene with 2 wt.% butene-1 was obtained in the form of a powder with a bulk density of 0.43 g/cm3.

Example 17 Gas phase copolymerization of ethylene with butene-1 in a fluidized bed reactor

The procedure was carried out exactly as in Example 16 except for the ratio (pC₄/pC₂) of 0.05.

Under these conditions, a copolymer of ethylene with 3.3 wt.% butene-1 was obtained in the form of a powder with a bulk density of 0.42 g/cm3.

Example 18 Gas phase copolymerization of ethylene with methyl-4-pentene-1 in a fluidized bed reactor

The procedure was repeated exactly as in Example 12, except for the use of the solid catalyst (P) in an amount equivalent to 0.8 milliatom of titanium, using 8 mmol of tri-n-octylaluminum at a temperature of 70°C with a mixture of ethylene, methyl-4-pentene-1 and hydrogen containing 10% (by volume) of hydrogen, the ratio (pC6/pC2) of the partial pressure of methyl-4-pentene-1 to that of ethylene being 0.05.

Under these conditions, a copolymer of ethylene with 4.8 wt.% methyl-4-pentene-1 was obtained in the form of a powder with a bulk density of 0.41 g/cm3.

Example 19 Gas phase co-transformation of ethylene with methyl-4- dentene-1 in a fluidized bed reactor

The procedure was repeated exactly as in Example 18 except for the ratio (pC₆/pC₂) of 0.1.

Under these conditions, a copolymer of ethylene with 9.5 wt.% methyl-4-pentene-1 was obtained in the form of a powder with a bulk density of 0.38 g/cm3. Table 1: Polymerization of ethylene Solid catalyst or solid product Temperature (ºC) % H2 (in volume) Productivity Density (g/cm³) Bulk density (g/cm³) (comparison) Table 2 Copolymerization of ethylene with 1-butene Solid catalyst or solid product Temperature (ºC) % H₂ in (volume) Productivity Density (g/cm³) % C₄ by weight in the copolymer Bulk density (g/cm³) (comparison) Table 3 Polymerization of ethylene solid catalyst Temperature (ºC) % H2 (in volume) Productivity Bulk Density (g/cm³) Comparison

Claims (13)

1. Catalyst for the polymerization or copolymerization of olefins, in particular ethylene, comprising a refractory oxide and atoms of chlorine, magnesium, titanium and/or vanadium, characterized in that it is a solid ethylene prepolymerized catalyst comprising per milliatom of titanium or vanadium, or titanium plus vanadium, 1 to 200 g, preferably 10 to 200 g, of polyethylene or a copolymer of ethylene with a small amount of an α-olefin containing 3 to 8 carbon atoms, 0.2 to 15 g of a refractory oxide, 1 to 10 mmol of magnesium, 0.1 to 20 milliatoms of aluminum or zinc, or aluminum plus zinc and 0 to a value less than 0.2 mmol of an electron donor compound. 2. Catalyst according to claim 1, characterized in that it is in the form of particles with a mass-average diameter of 50 to 500 µm and a bulk density of 0.25 to 0.6 g/cm³. 3. Process for preparing the catalyst according to claim 1 or claim 2, characterized in that it comprises 4 stages carried out in a liquid hydrocarbon medium consisting of at least one saturated liquid hydrocarbon: a) in a first step, bringing into contact a solid support based on a refractory oxide containing hydroxyl groups with a dialkylmagnesium of the general formula Mg R¹ R² optionally mixed and complexed with a trialkylaluminium of the general formula Al R³ R�sup4; R�sup5; where in the formulas R¹, R², R³, R⁴ and R⁵ represent identical or different alkyl radicals having 1 to 12 carbon atoms, b) in a second stage, bringing the product from the first stage into contact at a temperature in the range from 0°C to 90°C with an organic monochloro compound, selected from secondary or tertiary alkyl or cycloalkyl monochlorides having 3 to 19 carbon atoms and from compounds of the general formula R⁹9; R¹⁰ R¹¹ CCl, where R⁹9; is an aryl radical having 6 to 16 carbon atoms and R¹⁰ and R¹¹ are identical or different radicals selected from hydrogen, alkyl radicals having 1 to 6 carbon atoms and aryl radicals having 6 to 16 carbon atoms, which are identical or different with respect to R⁹9; c) in a third step, bringing the product obtained from the second step into contact with at least one tetravalent titanium or vanadium compound or a trivalent vanadyl compound and d) in a fourth stage, bringing the product obtained from the third stage into contact with ethylene or ethylene mixed with an α-olefin containing 3 to 8 carbon atoms, in the presence of at least one activating agent, selected from organoaluminium and organozinc compounds, in such amounts that a solid catalyst in the form of a prepolymer containing 1 to 200 g of polymer per milliatom of titanium, or vanadium, or titanium plus vanadium, is obtained, the molar ratio of the amount of the metal(s) (Al and/or Zn) of the activating agent to the amount of titanium or vanadium, or titanium plus vanadium being 0.3 to 10. 4. Process according to claim 3, characterized in that each gram of the carrier is brought into contact with 0.1 to 7.5 mmol of dialkylmagnesium or dialkylmagnesium plus trialkylaluminum. 5. Process according to claim 3 or 4, characterized in that the organic monochloro compound has the general formula R⁶ R⁷ R⁷ C Cl, where R⁶ and R⁷ are the same or different alkyl radicals containing 1 to 6 carbon atoms and R⁸ is a hydrogen atom or an alkyl radical having 1 to 6 carbon atoms and R⁶ and R⁷ are the same or different. 6. Process according to claim 3 or 4, characterized in that the organic monochloro compound is sec-propyl chloride, sec-butyl chloride, tert-butyl chloride, benzyl chloride, 1-phenyl-1-chloroethane, cyclohexyl chloride or 1-methyl-1-chlorocyclohexane. 7. Process according to one of claims 3 to 6, characterized in that the solid catalyst is obtained in the form of a prepolymer containing 10 to 200 g of polymer per milliatom of Ti, or V, or Ti plus V. 8. A process according to any one of claims 3 to 7, characterized in that the product obtained from the first stage is brought into contact with the organic monochloro compound in an amount such that the molar ratio of the amount of organic monochloro compound to the amount of magnesium, or magnesium plus aluminum, contained in the product resulting from the first stage is 1 to 3.5. 9. Process according to one of claims 3 to 8, characterized in that the product obtained from the second stage is brought into contact with the titanium and/or vanadium compound(s) in an amount such that the atomic ratio of the amount of titanium, or vanadium, or titanium plus vanadium, to the amount of magnesium, or magnesium plus aluminium, contained in the product resulting from the second stage is 0.1 to 0.9. 10. Process according to one of claims 3 to 9, characterized in that the titanium or vanadium compound is selected from a tetravalent titanium compound of the general formula Ti(OR)m X4-m a tetravalent vanadium compound of the general formula V (OR)m X4-m and a trivalent vanadyl compound of the general formula VO (OR)n X3-n where in the general formulas R is an alkyl radical with 2 to 6 carbon atoms, X is a chlorine or bromine atom and m is an integer or fraction, equal to or greater than 0 and less than 4 and n is an integer or fractional number equal to or greater than 0 and less than 3. 11. Process according to one of claims 3 to 10, characterized in that in the third stage the product obtained from the second stage is first treated in its entirety with at least one titanium or vanadium compound selected from a tetravalent titanium compound of the general formula Ti(OR)p X4-p a tetravalent vanadium compound of the general formula V (OR)p X4-p and a trivalent vanadyl compound of the general formula VO (OR)q X3-q where in the general formulas R is an alkyl radical with 2 to 6 carbon atoms, X is a chlorine or bromine atom, p is an integer or fraction equal to or greater and less than 2 and q is an integer or fraction equal to or greater than 0 and less than 1.5, and then with at least one titanium or vanadium compound selected from a tetravalent titanium compound of the general formula Ti(OR)r X4-r a tetravalent vanadium compound of the general formula V (OR)r X4-r and a trivalent vanadyl compound of the general formula VO (OR)s X3-s where in the general formulas R and X have definitions same as above, r is an integer or fractional number equal to or greater than 2 and less than or equal to 4 and 5 is an integer or fractional number equal to or greater than 1.5 and less than or equal to 3, is brought into contact . 12. Process for the polymerization of ethylene or copolymerization of ethylene with at least one α-olefin containing 3 to 8 carbon atoms in the presence of the catalyst according to claim 1 or 2. 13. Process according to claim 12, characterized in that the copolymerization of ethylene with at least one α-olefin containing 3 to 8 carbon atoms is carried out in the gas phase, in the presence of at least one cocatalyst selected from organoaluminum and organozinc compounds, at a temperature of 20°C to 110°C, under a total pressure of 0.5 to 5 MPa, the ratio of the partial pressure of the α-olefin(s) to that of ethylene being 0.01 to 0.5.